The Environment Southland chairwoman who placed a hoax call to Invercargill mayor Tim Shadbolt on a live TV show has gone on leave for six weeks.

It was revealed today that Ali Timms was the "struggling mother" who harangued Shadbolt for almost 10 minutes. Timms admitted the deception when confronted by a journalist yesterday but said it was done as a practical joke.

Today, her fellow Environment Southland council members said it was an "unacceptable lapse of judgment".

They held a session in committee at their final meeting of the year, with acting chairman Nicol Horrell issuing a statement afterwards.

"Councillors have unanimously expressed their extreme disapproval of the unacceptable lapse of judgment shown by chairwoman Ali Timms in taking part in the Invercargill City Council's televised talkback programme under an assumed name last week.

"Councillors have accepted Cr Timms' application for six weeks leave of absence, effective immediately. We expect to hold an extraordinary meeting... to consider the council's chairmanship in late January."

The call was made to the city council's live talkback show on Cue TV last Wednesday night. Timms claimed to be "Ruby", a mother of two who was struggling to make ends meet after her husband had been laid off from the Tiwai Point aluminium smelter.

She repeatedly asked Shadbolt questions about the planned Auckland-to-Bluff yacht race which is being promoted by the city council, saying it was a huge risk to city ratepayers and questioning what benefits ratepayers would get from it and what analysis the council had done.

"Ruby" indicated that if the council wanted to do something to support Bluff it should look to sprucing up the port town's main street.

Shadbolt appeared uncomfortable with the intensity of the questioning, but appeared to have at least an inkling of the true identity of the caller, at one stage calling her Ali, at which she replied, "Sorry, who . . . this is Ruby here".

During the conversation, Shadbolt told "Ruby" he had talked to Ali Timms about the issue and that she was understanding about what a project like the yacht race could mean for the city.

Timms appears to have tried to disguise her voice during the phone-in, by blocking her nose, and almost gave the game away at the start of her call when the receptionist asked for the phone number she was calling from for the show's records. Timms read out all the correct numbers on her cellphone except the final digit.

When confronted Timms said she had done it as a "bit of a practical joke, that was all".

"I could tell Tim knew who it was because he called me by my name, so end of story."

When asked if she had two children and a partner who had been laid off at Tiwai, she reiterated it had been a practical joke and a "few laughs".

"Tim knew who it was, he didn't seem too bothered about it and that's all I have to say."

She declined to comment and hung up when asked whether she had contacted Shadbolt afterwards to tell him she had been "Ruby".